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D.7.7 Electrical Power Systems
The cumulative pollution burden of producing electricity is three times that of a building’s electrical load at the building site. Ensuring efficient transfer and consumption of electricity within a building will save money, because less electricity is needed, and will reduce the amount of pollutants emitted at the power plant to produce the electricity that the building consumes. Improve the efficiency of building electrical power systems by:
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Using higher voltage power distribution systems in buildings, such as 480/277 volts where electric codes allow. High-voltage distribution systems can result in better economics, smaller conductor sizes, and less energy consumed in the system due to lower line losses.
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Sizing transformers as close as possible to the actual anticipated load to avoid oversizing and to minimize fixed thermal losses. When possible, distribute electric power at the highest practical voltage and power factor consistent with safety.
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Comply with the National Energy Managers Association (NEMA) criteria for premium transformers to reduce the no-load (core) losses and the coil (winding) losses during transformer operation. The resulting energy savings will range from about 30 percent at no-load to about 10 percent at full load. Always specify ENERGY STAR® transformers.
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Specify higher-efficiency, liquid-filled transformers. These transformers typically use oil as a combination coolant and insulating medium and they are most frequently installed outdoors.
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Select energy-efficient electrical motors to reduce building electricity consumption. It is best if all motors one horsepower and larger are three-phase and “NEMA Premium.”
Fort Carson experiences excellent solar resources. For this reason, consider integrating solar electric systems (PV), into the design of new buildings. PV panels produce DC electricity from sunlight. If AC power is required, an inverter converts the DC electricity to AC. PV electricity is not currently cost-effective for most applications at Fort Carson because of the low cost of grid electricity. These systems can be cost-effective for applications where the power grid location is more than 1⁄4 mile away from the building site and when trenching would otherwise be required to bring power to signs or outdoor lighting.
The lifetime operating cost of PV systems is low and these systems can help protect Fort Carson from future electricity shortages.
D.7.7.1 Uninterruptible Power Supply (UPS) Systems
Uninterruptible power supply (UPS) systems provide electricity when grid power fails. UPS systems consist of rectifiers, battery storage, inverters, and controls to convert AC electricity to DC for the storage batteries, and back to AC for the load. The batteries are typically sized to meet the load for 10 to 15 minutes. All UPS systems consume energy to maintain a charge in the batteries. Avoid UPS systems unless the mission requires them.
Two types of UPS systems exist: on-line UPS and standby UPS. An on-line UPS feeds the entire load through a rectifier to a DC bus that serves the batteries. The DC power is converted to AC power to serve the load. This design eliminates grid disturbance; however, it is less efficient than the standby design because the entire load passes through a rectifier and an inverter.
If an on-line UPS system is chosen, it can be augmented with solar electric (PV), power at the DC bus voltage. This arrangement saves the inverter cost in a grid-tied PV system. It also provides a longer run time for the UPS system if the power failure occurs during the daytime because the PV system will feed part of the load.
A standby UPS system exposes the load to utility power during normal operation, if utility power fails a switch transfers the load to the UPS system until the utility power becomes available. A standby type UPS cannot readily accept PV augmentation because the load is not normally served by the UPS.
D.7.7.2 Green Power Procurement
Purchasing “green power” is one way to minimize the environmental burden of using electricity generated using fossil fuels. Purchasing green certificates (also known as green tags, renewable energy certificates, or tradable renewable certificates [TRC]) represent the environmental attributes of power generated from renewable electric plants. Several organizations offer TRCs. The approximate cost of TRCs is 2¢/kWh. These certificates support power generation from newly developed power generation facilities that use renewable energy technologies (power from the sun, wind, geothermal, low-impact hydropower, or biofuels). For more information see: www.green-e.org.
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